1. Field of the Invention
Embodiments of the present invention generally relate to the processing of photovoltaic cells. In particular, embodiments of the present invention relate to apparatus and method for laser ablation of portions of material layers from a side of the photovoltaic cell.
2. Description of the Related Art
Photovoltaic (PV) devices or solar cells are devices converting sunlight and other light into electrical energy. Usually solar cells consist of a semiconductor material—mostly manufactured from silicon that has n-doped or p-doped semiconductor regions. The most common solar cell material is silicon, which is in the form of single crystal, polycrystalline or multicrystalline substrates, sometimes referred to as wafers. Solar cells may be tiled into larger solar arrays. The solar arrays are created by connecting a number of solar cells and joining them into panels with specific frames and connectors. Because the amortized cost of forming silicon-based solar cells to generate electricity is higher than the cost of generating electricity using traditional methods, there has been an effort to reduce the cost to form solar cells.
A crystalline solar cells generally includes a plurality of conductive and dielectric materials deposited on a substrate to form solar cell devices. Since crystalline solar cell substrates are generally quite thin, it is thermo-mechanically advantageous to include a passivating layer between the rear surface aluminum electrode layer and the silicon substrate. In order to increase cell efficiency, various approaches, such as laser-fired contacts (LFC) have been proposed as an ideal manner to realize contact holes for a passivated rear surface by driving the aluminum through the passivating layer several microns deep into the silicon substrate, thereby creating a localized Al/Si alloy contacts without severe damage to the passivating layer.
However, the laser system that accomplish LFC process are typically stand-alone systems that require additional substrate handling steps to transfer the solar cell substrates from a different processing system to the laser system. Since the thickness of the solar cell substrate are getting extremely thin and fragile, any additional handling steps are usually not desirable in order to minimize a breakage rate in association with each substrate handling step.
Therefore, there is a need for improved laser ablating process and apparatus for removing material from solar cell substrates without any additional substrate handling steps.